1. Technical Field
The present invention relates to an optical information processing apparatus, an optical information servo controlling method, an optical information recording method, and an optical information reproducing method, and more particularly, to an optical information processing apparatus, an optical information servo controlling method, an optical information recording method, and an optical information reproducing method capable of recording and reproducing optical information at multiplexed angles by using different offset angles corresponding to different tracks, recording and reproducing the optical information by changing an incidence angle of a reference beam beyond a limit angle range into an incidence angle within the limit angle range, and performing servo control by using optical information of neighborhood readout beams reproduced from neighborhood tracks.
2. Related Art
As an example of an optical data processing apparatus, there are DVDs (Digital Versatile Disc), HD-DVDs, BDs (Blue Ray Disc), near field optical processing apparatuses, and holographic optical information processing apparatuses.
The holographic optical information processing apparatus irradiates a reference beam on a recording medium to form interference fringe by intersection of the reference beam and an optically modulated signal beam, so that optical information (or data) is recorded on the recording medium. In order to reproduce the data recorded on the recording medium, only the reference beam is irradiated to the interference fringe on recording medium. A readout beam generated by diffraction of the interference fringe is detected and output, so that the data recorded on the recording medium can be reproduced.
In such a holographic optical information processing apparatus, the reference beam may be irradiated on one beam spot at different angles in a multiplexed manner in order to increase data recording capacity. The multiplexed input data can be output by irradiating only the reference beam at different angles at the time of data reproduction. In other words, the holographic optical information processing apparatus is an large capacity data storage apparatus capable of inputting and outputting multiplexed and overlapped data in one beam spot.
In such a holographic optical information processing apparatus, an optical multiplexing method is used to increase data recording density. As examples of the optical multiplexing method, there are an angular multiplexing method, a phase-code multiplexing method, a wavelength multiplexing method, a shift multiplexing method, and the like. In the angular multiplexing method, the multiplexing is performed by changing an incidence angle of the reference beam. In the phase-code multiplexing method, the multiplexing is performed by spatially modulating phases. In the wavelength multiplexing method, the multiplexing is performed according to a change in wavelength by using a wavelength variable laser. In the shift multiplexing method, the multiplexing is performed by shifting the recording medium.
At the time of reproduction of the multiplexed, recorded optical information, the optical information may be reproduced from neighborhood recording regions as well as the selected recording region. In this case, the optical information reproduced from the non-selected recording regions becomes noise, so that the reproduction efficiency of the optical information reproduced from the selected recording region may deteriorate. In order to solve the problem, techniques for blocking the readout beams reproduced from the non-selected recording regions have been proposed. As an example, one of the techniques is disclosed in International Patent Publication No. WO 2004/102541, titled “High Data Density Volumetric Holographic Data Storage Method And System” by Thomson Licensing Inc. In the Patent Document, the readout beams reproduced from the non-selected recording regions are blocked by using a filter.
On the other hand, servo control is needed in order to accurately reproduce the recorded holographic optical information. A technique therefor is disclosed in US Patent Application Publication No. 2005-0030876, titled “Optical Information Recording Apparatus And Optical Information Reproducing Apparatus” filed by Optware Corporation in Japan. In the Patent Document, a separate laser source for servo control is used.
In the technique disclosed in the Patent Document, since the separate laser source for servo control is used, constructions of optical systems and apparatuses for servo control become complicated. In addition, since the laser source for servo control uses a wavelength different from that of the optical information processing apparatus, constructions of the optical information recording medium or the optical information processing apparatus become more complicated.